Quantitation of tissue calpain activity after isolation by hydrophobic chromatography

A rapid and reliable method for quantitating tissue calpains (Ca2+-activated, neutral, thiol proteases) was developed using hydrophobic chromatography with phenyl-Sepharose. Calpains I and II isolated by this method are free of endogenous inhibitor(s) (calpastatin), activator(s), and nonspecific proteases. These calpains expose hydrophobic regions in the presence of Ca2+ and bind tightly to phenyl-Sepharose. Inactivation of bound calpain is prevented by the addition of leupeptin (20 microM). Calpains I and II bound initially by phenyl-Sepharose in a Ca2+-dependent manner are then eluted successively on the basis of their Ca2+-independent binding to phenyl-Sepharose. Because calpastatin may prevent binding of calpain to phenyl-Sepharose by forming a protease-inhibitor complex in the presence of Ca2+, preadsorbing the protease to a suspension of phenyl-Sepharose beads initially in the absence of Ca2+ separates most of the calpain present in tissue extracts from calpastatin. The isolated calpains obtained are assayed by casein digestion. This quantitation procedure is suitable for measuring calpain activity in various tissues and cells including erythrocytes.

Monovalent cation-insensitive hydrophobic region on calmodulin facilitates the rapid isolation and quantitation of calmodulin free from other Ca2+-dependent hydrophobic proteins

Calmodulin binds quantitatively to phenyl-Sepharose through its Ca2+-induced hydrophobic binding region. Troponin C and S-100 protein, as well as several other proteins present in rat tissues, also bind to phenyl-Sepharose in a Ca2+-dependent manner. While the Ca2+-dependent binding of calmodulin to phenyl-Sepharose is not altered appreciably by monovalent cations, they do appear to compete for Ca2+ binding to most of the other proteins, including S-100 protein, which exhibit Ca2+-induced interaction with phenyl-Sepharose. The selective elution of these proteins from the phenyl-Sepharose column can be achieved with a 0.5 M concentration of monovalent cations such as K+, Na+, and NH4+ in the presence of a low (100 microM) Ca2+ concentration. Calmodulin-binding proteins associated with calmodulin in crude cell extracts can prevent the interaction of calmodulin with the phenyl-Sepharose, resulting in low recoveries of calmodulin from these tissues. The majority of these interfering proteins are heat labile so that heat treatment (boiling) of the cell extract for a limited time (5 min) negates any binding of these proteins to calmodulin and allows the quantitative recovery of calmodulin by hydrophobic interaction chromatography. This procedure allows the rapid and quantitative recovery of highly purified calmodulin from both cytosolic and Triton X-100-solubilized particulate fractions prepared from various rat tissues. Calmodulin isolated in this manner can be accurately and reliably quantitated by direct protein determination with Coomassie brilliant blue dye or fluorescamine or by the cyclic nucleotide phosphodiesterase stimulation assay.

The effects of chemical modification of calmodulin on Ca2+-induced exposure of a hydrophobic region. Separation of active and inactive forms of calmodulin

Native calmodulin binds four calcium ions per molecule and exhibits strong Ca2+-dependent binding to phenyl-Sepharose. In contrast, calmodulin inactivated by oxidation of methionine residues or by deamidation binds fewer calcium ions (two per molecule) and shows relatively weak interaction with phenyl-Sepharose. Calmodulin inactivated by modification of lysine residues still is able to bind four calcium ions per molecule and shows strong binding to phenyl-Sepharose similar to native calmodulin. The results suggest that complete exposure of calmodulin's hydrophobic region occurs only after the binding of four ions of calcium to the calmodulin molecule. Thus, phenyl-Sepharose hydrophobic interaction chromatography might be used to separate active calmodulin from inactive forms of calmodulin obtained by oxidation or heat treatment for prolonged periods. As an example, phenyl-Sepharose chromatography can be used to separate free iodide and inactivated species of calmodulin readily from the active, iodinated form of calmodulin following iodination.

Calmodulin interacts with cyclic nucleotide phosphodiesterase and calcineurin by binding to a metal ion-independent hydrophobic region on these proteins

Hydrophobic interaction chromatography is employed to determine if calmodulin might associate with its target enzymes such as cyclic nucleotide phosphodiesterase and calcineurin through its Ca2+-induced hydrophobic binding region. The majority of protein in a bovine brain extract that binds to a calmodulin-Sepharose affinity column also is observed to bind in a metal ion-independent manner to phenyl-Sepharose through hydrophobic interactions. Cyclic nucleotide phosphodiesterase activity that is bound to phenyl-Sepharose can be resolved into two activity peaks; one peak of activity is eluted with low ionic strength buffer, while the second peak eluted with an ethylene glycol gradient. Calcineurin bound tightly to the phenyl-Sepharose column and could only be eluted with 8 M urea. Increasing ethylene glycol concentrations in the reaction mixture selectively inhibited the ability of calmodulin to stimulate phosphodiesterase activity, suggesting that hydrophobic interaction is required for activation. Comparison of the proteins which are bound to and eluted from phenyl- and calmodulin-Sepharose affinity columns indicates that chromatography involving calmodulin-Sepharose resembles hydrophobic interaction chromatography with charged ligands. In this type of interaction, hydrophobic binding either is reinforced by electrostatic attractions or opposed by electrostatic repulsions to create a degree of specificity in the binding of calmodulin to certain proteins with accessible hydrophobic regions.

A simplified procedure for the estimation of arginine in plasma and urine using arginase

To ensure reliable arginine estimation, other compounds giving positive results with Chinard's ninhydrin reaction were removed by simple ion-exchange chromatography. Eluted arginine was converted to ornithine by arginase and estimated using Chinard's ninhydrin reaction. Plasma arginine level in adults was in the range 56--98 mumol/l, and urine arginine in the range 0.58--1.77 mg/day.

Suicide--a retrospective study in a culturally distinct community in India

Occurrence and features of 130 suicide cases were studied in a culturally distinct community, Goa (India), which was isolated from mainland for over 450 years records obtained from the police and information collected from close relatives of the deceased were analyzed retrospectively. It was noted that cultural and religious factors continue to play an important role in suicidal behaviour in India. The rate was higher for males as compared with females and was greater in joint family than in nuclear family. Similarly, married persons of both sexes had a higher frequency. Ethnically the rate among Hindus was higher than among Christians. Mental illness constituted a major cause of suicide, followed by domestic conflicts. An interesting feature observed in the study was that more persons commit suicide in their own birth place and near their own homes.